[{quoted}](name=The JigSAW,realm=NA,application-id=3ErqAdtq,discussion-id=MeaXTrwx,comment-id=0002,timestamp=2017-03-12T01:20:07.000+0000)
I've always thought his kit allowed him way too much ability to just take somebody out quickly with little if any risk of dying, because if he had a risk of dying he'd just ult and walk off invisible for 20-30 seconds.
I wouldn't call him cancer though. Earlier I had to fight a Rengar as Wukong top and it wasn't a fun match whatsoever, but I built sunfire and randuin's omen and then when he leapt out of the bush at me, I used the omen active while Q/E and then ulting which did the trick. He was able to kill me simply by staying in the bush and leaping at minions to gain his stacks, but since they now drop off he had to get all four to hold a little longer. So, after he got me I refused to engage at all while I built armor and health. After that, I was able to put him down even when he had 8 kills and I had 1. I barely play Wukong so if it was the wrong combo, that'd be why.
Best things to buy vs Rengar as quickly as possible:

That'll give you over 200 armor and 1,000 health as well as the ability to reflect his basic attacks as magic damage to him (with 50 armor and 15% of his damage) every basic. Use omen's active when he's low and about to stealth and jump him.
When you think about cancer though, Rengar doesn't have double crit, a shield that regenerates in combat, a wind wall, and 50% bonus armor pen for 15 seconds on ult regardless if it hits/kills or not and a dash that can be spammed every tenth of a second. Just saying, there's worse to deal with.
In my experience with Wu, it is far better to go flat damage and roam. You'll still do decent damage against their ADC's, and having your stealth mean's you'll be able to use it. Maybe you only do 50% of their health because you're behind, but they'll only have 50% of their health left after fighting your laner.
Then you outscale almost any assassin because your invisibility means you burst them before they can burst you. That includes Rengar - you know where he is? Press W, E+auto+Q+R and he's dead. Well, Rengar W might change that, but he's probably dead.
Reference: Going 1/6 against a Jayce then oneshotting him while not taking any damage later on.
However, this means you don't get much farm. But your Q means last hitting under tower is simple enough, along with building AD. Just don't let them make a freeze.